What is an INR?

International Normalized Ratio (INR) is the specific blood test used to measure the time it takes for blood to form a blood clot. This is called a prothrombin time test, or protime (PT). The PT is reported as the International Normalized Ratio (INR). The INR is a calculation based on results of a PT test and is used to monitor individuals who are being treated with the anticoagulation medication warfarin. INR tests are used instead of the PT because the INR is corrected for the strength of your blood clotting tissue. INR is also used to standardize the method used across all labs to lead to the most accurate results.

  • If a person’s INR is too low, blood clots may not be prevented
  • If a person’s INR is too high, they may experience uncontrolled or dangerous bleeding.